Sub-quadratic dependence of visible upconversion on infra-red direct luminescence decay owing to static energy-transfer upconversion

Because of their broadband luminescence, TM-ion-doped materials are of high interest for applications as tunable and short-pulse lasers. Systems with a d1 electron configuration possess only one excited 3d level and excited-state absorption into higher-lying 3d levels is impossible. One of these d1 systems, Ti:sapphire has become the most successful tunable and short-pulse laser system to date. Mn6+ is a promising d1 ion for a tunable laser system. In BaSO4, near-infrared emission from Mn6+ was observed. The room-temperature stimulated-emission cross section is larger than the excited-state-absorption cross section in the spectral range 920-1600 nm [1], i.e., as a laser material BaSO4:Mn6+ can offer a broad tuning range.\ud Here we report on the first epitaxial growth of Mn6+-doped BaSO4 layers. Growth techniques such as the melt growth fail, because barium sulphate has a phase transition at 1090°C and exhibits thermal decomposition at 1590°C. Therefore, we grew BaSO4 substrate crystals by the flux method. The Mn6+ ions tend to reduce to Mn5+ at T  620°C. We used a CsCl-KCl-NaCl solvent [2] for the LPE of BaSO4:Mn6+. This solvent has a low solidification temperature of 480°C and the growth process could be performed at temperatures well below 620°C. The nominal Mn6+ concentration was up to 0.8 mol%. High quality, lack of large-size inclusions, and low defect concentration were achieved. These Mn6+-doped BaSO4 layers were investigated spectroscopically by absorption, emission, and luminescence-excitation measurements at room temperature. Excitation at 800 nm leads to broadband Mn6+ emission between 850 and 1600 nm. Currently, we investigate the lasing potential of our BaSO4:Mn6+ layers.\ud [1] T.C. Brunold, H.U. Güdel, S. Kück, G. Huber, JOSA B 14, 2373 (1997).\ud [2] D. Ehrentraut, M. Pollnau, J. Cryst. Growth 234, 533 (2002)

Oscar Gelderblom, Cities of Commerce. The Institutional Foundations of International Trade in the Low Countries, 1250 -1650

Oscar Gelderblom, Cities of Commerce. The Institutional Foundations of International Trade in the Low Countries, 1250 -1650 (Princeton nj: Princeton University Press, 2013, 312 pp., isbn 978 0 691 16820 3).</p

‘The greatest marketplace in the world’ : the role of Antwerp in the economic and financial network of the Habsburg Empire

The city of Antwerp played a crucial role in the history of the Habsburg Empire of Charles V as a distribution center of long-distance trade, where colonial products, such as sugar, spices and precious metals were exchanged against textiles and a broad variety of luxury commodities. At the same time it was of great importance as a financial center, where the emperor could find the necessary credit for its ambitious political plans. Antwerp had a long tradition as port city as well as a center of fairs, but it was at the onset of the sixteenth century, that it christallized as the meeting point of the leading commercial actors of the moment, the Portuguese, who had just discovered the maritime route to India, the Southern Germans, with the precious metals they imported from the Alps and Central Europe, the English with their cloth, together with Spaniards, Italians and many others. During its Golden Age, Antwerp became a thriving metropolis, of more than 100 000 inhabitants, thousands of merchants, both foreign and local, artisans, and numerous outstanding artists and intellectuals. The municipal government made great efforts to provide the city with an adequate infrastructure, both in terms of architecture, by building new city walls or port infrastructure, as well as in terms of commercial institutions. The splendor of Antwerp was such that many contemporaries spoke of it in utmost admiration. However the religious and political conflicts of the late sixteenth century brought its Golden Age to a sudden end, only few years after reaching its apogee. As a result of the Dutch Revolt, many merchants left Antwerp, the city lost almost half its population and its commerce declined. In the seventeenth- and eighteenth century, Antwerp remained a port city with a considerable commercial and financial activity, but it would in no way equal places such as Amsterdam and London

Narrativas com alternâncias de código em contexto escolar de uma comunidade multilíngüe

This article analyzes two oral narratives produced in a school in Santa Maria do Herval (RS). These narratives are peculiar because of the frequent code switching, sometimes from Portuguese to standard German, sometimes from standard Portuguese to the dialectal variety spoken in that particular community. The first narrative to be analyzed is produced in the story telling time, in which the librarian tells the children a story from a picture book, switching the code between Portuguese and German. The second narrative is a story told by the class teacher during talking in circle, also based on a picture book. The code switching in this narrative involves teacher/pupils interaction directly. The use of both languages is, as mentioned by Breunig (2005), a cultural responsive pedagogy, since the language spoken at home by most children is being positively valued at school. Furthermore, teachers’ practices are close to those carried out by the children at home